"Both in Britain in the United States, women born around 1940 were the first generation in which many smoked substantial numbers of cigarettes throughout adult life," Richard Peto of the University of Oxford said in a statement. "Hence, only in the 21st century could we observe directly the full effects of prolonged smoking, and of prolonged cessation, on premature mortality among women."
Two-thirds of all deaths of smokers in their 50s, 60s, and 70s are often due to smoking-related diseases, including lung cancer, chronic lung disease, heart disease and stroke.
However, the study, published in The Lancet, found women who stopped smoking at about age 30 reduced their risk of premature death to due to cigarettes by 97 percent.
The Million Women Study recruited 1.3 million women in Britain ages 50 to 65 from 1996 to 2001. Participants completed a questionnaire about their lifestyle, medical and social factors and then took another survey three years later.
At the start of the study, 20 percent of the study participants were smokers, 28 percent were ex-smokers and 52 percent had never smoked.
The researchers found women who were still smokers when surveyed three years later were nearly three times as likely as non-smokers to die over the next nine years.